We're looking into providing an alternative visualization layer based on WPF/Silverlight. That would make it easier to implement some features we have on our request list, including zooming and scaling. It's still in the investigation phase,
however.

This is a great start! It's about time Excel had network analysis functionality and the current implementation is already better in some ways than many of the exisitng dedicated packages. The one thing I'd add to the wishlist is greater control over
vertix labels. I work with country-by-country networks and I often use a circular node layout. The problem with most packages, including NetMap (for now), is that they place all node labels in the same positions. In a circle layout, this places many of
the labels on the inside of the circle, where they are hidden by or themselves hide the edges. Your primary label option fixes this problem, but introduces another one: the rectangular vertix boxes obscure some of the edges, which makes it tough to tell which
edge connects which vertices (this is particularly true for the vertices located near one another in the circle). The way out of all this, would be to enable context-sensitive labeling, which would automatically try to stay out of the way of the edges. A
simpler solution would be to introduce a special label option for the circular layout, which rotates the labels in increments to create a spoke pattern on the outside of the circle. Just a thought.

Great work Tony and Marc! Is there a way to suppress arrowheads? I would like to show some edges without them. Alternatively if we could size arrowheas smaller than the width of the line that would effectively suppress them.

Second issue-- is "skip" the way to exclude unwanted nodes from visualization?

Relatedly, is there an easy way to extract a subset of nodes along with all of the incident edges into a new worksheet?

Undirected graphs will not display arrow heads (and several network metrics will be calculated differently) if the toggle for directed and undirected graphs is selected in the ribbon.

Skipping selected nodes is simple to do with a formula in the "Visibility" column. Try something like =IF(CellRef=Condition,1,0) to test if a cell meets a condition. If the condition is true, place a "1" in the cell, if the
condition is false, place a "0" in the cell. Any row with a Visibility = 0 will not be displayed.

Your request for a feature that could be called "Remove all non-selected nodes" is a good one and we will add it to the feature request list.

Our vertex labelling is weak right now, as you've discovered. The labels always go in the same location with respect to the vertices, which sometimes works but often doesn't.

Automated label location with maximum visibility is a difficult problem in the general case. We do have a work item, however, that will offer control over the location of each label. And I just amended that work item with your suggested solution
for the circular layout case, which sounds like a good idea.

To expand on Marc's reply: There is an option to control the size of the arrowheads. In the graph pane, click the Options button, then look for the "Arrow size" box. Arrows are sized relative to the edge width, so increasing the
edge width also increases the arrow size.

Setting a Visibility cell on the Vertices worksheet to "Skip (0)" or "0" causes that vertex and any edges that contain the vertex to be skipped. "Skip" means "don't read this row into the graph." You can get
more details on this by hovering over the yellow "How Vertex Visibility Works" and "How Edge Visibility Works" comments in the workbook.

You can use Excel's table filtering feature (the down-arrows to the right of each table column header) to filter out unwanted rows, and then copy-and-paste the remaining rows to a new worksheet. However, if you do this on the Vertices worksheet,
the filtered-out vertices will probably still be present in the Edges worksheet, so this won't give you the results you want. I've added your request to our feature request list.